1. Field of the Invention
The present invention relates to an image processing apparatus for detecting a specific region in an observation image, and an image processing program which can be provided as a computer program product, and more particularly to an image processing apparatus and an image processing program for detecting a specific region in a sequence of observation images which individually show at least one observation target among plural types of observation targets, or a specific region in a sequence of observation images picked up from different imaging distances.
2. Description of the Related Art
As a system for obtaining a sequence of observation images which individually show at least one observation target among plural types of observation targets, a capsule endoscope, for example, which serves to observe an interior of a subject has been developed. The capsule endoscope has an imaging function and a radio communication function. After being swallowed by a subject, the capsule endoscope moves through the interior of esophagus, stomach, small intestine, large intestine, and the like, following peristaltic movements or the like while sequentially picking up images and sequentially transmitting image data generated by the image pickup to an external receiver by radio communication and the like until naturally discharged. Doctors, nurses, and the others can display the image data the external receiver acquires as an observation image and observe the interior of the subject based on the observation image.
Generally, the capsule endoscope acquires an enormous number of observation images in sequence, which demands doctors, nurses, and others to put significant amount of time and energy for the observation based on the sequence of observation images. Meanwhile, an abnormality detecting system (such as one described in Published Japanese Translation of International Patent Application No. 2004-521693 (Kohyo)) is developed to allow detection and display of abnormal areas in an observation target and efficient observation of affected areas based thereon. The abnormality detecting system divides observation images into plural unit blocks and compares color information of each unit block with a previously-prepared color reference of abnormal area and a previously-prepared color reference of normal area to detect abnormal areas.
In the sequence of observation images acquired by the capsule endoscope, each organ appears in significantly different brightness and color from other organs depending on its type; for example, the small intestine appears in murkier colors than the stomach because of the influence of mucus, content, and the like. Further, the characteristics of the abnormal area, which is a detection target, are different for each type of organ. For example, an enlarged blood vessel in the small intestine is an abnormal area which should be detected, while a blood vessel in the stomach is an abnormal area which does not need to be detected preferentially. Thus, some abnormal areas are organ-dependent.
In the sequence of observation images acquired by the capsule endoscope, each observation image of the same abnormal area in the organ is picked up from different imaging distance because the capsule endoscope, which serves as an imaging device, picks up the images while moving through the organs. Thus, image regions corresponding to the same abnormal area are in different sizes (areas) and colors in respective observation images according to the imaging distances, and thereby exhibit different features.